The present invention relates to a cylinder head gasket placed between two members such as a cylinder head and a cylinder block of an internal combustion engine.
When joint surfaces between a cylinder head and a cylinder block (cylinder body) of an automobile engine are sealed, a metal cylinder head gasket is placed between the cylinder head and the cylinder block to seal combustion gas, coolant water, and lubrication oil.
Such a cylinder head gasket has been changed from a laminated type having many layers of metal plates to a simple structure type composed of one or two metal plates for reducing a weight and production cost of an engine. Since only one or two structural plates are used, usable materials are limited for reducing a weight of an engine. A type and the number of sealing methods are limited, so that it is necessary to use a relatively simple sealing method.
As a weight and size of an engine have been reduced recently, the engine tends to have lower rigidity. Upon sealing with the cylinder head gasket, when a large sealing surface pressure is applied around a cylinder bore, the cylinder bore tends to deform. Accordingly, it is difficult to obtain sufficient sealing performance.
A laminated metal gasket 1X has been proposed, for example, as shown in FIG. 5 (see Patent Reference 1). Plural beads formed of a first bead 6X and a second bead 2X encircle a hole H to be sealed, and is sequentially shifted from the hole H. Top portions of the full beads 6X and 2X alternately face in opposite directions. That is, two bead plates, i.e., a first bead plate 8X and a second bead plate 2X, are overlapped such that the bead plates protrude inwardly with each other. The first bead plate 8X is folded at a side of the hole H, which is overlapped with the second bead plate 2X.
With this structure, it is possible to increase a portion of the bead for generating a surface pressure to a desired width. Accordingly, it is possible to reduce a thickness of the gasket and improve sealing performance.
However, in such a structure, the second hull bead 2X of the second bead plate 4X enters the folded portion of the first bead plate 8X. Accordingly, a pressure generated with the second bead plate 4X interferes with a pressure generated with the first bead plate 8X. As a result, when a primary sealing portion formed of the first full bead 6X and the folded portion and a secondary sealing portion formed of the second full bead 2X are designed to obtain a specific pressure distribution around the hole H to be sealed, it is necessary to consider the interference, thereby making it difficult to design and produce the cylinder head gasket. Therefore, the cylinder head gasket with such a structure may not be able to sufficiently seal a cylinder bore of a recent engine with lower rigidity and a smaller size.
Patent Reference 1: Japanese Utility Model Publication (Kokoku) No. 04-33490.
In view of the problems described above, an object of the present invention is to provide a cylinder head gasket for an engine with low rigidity and a high maximum pressure (Pmax), in which it is possible to improve a secondary sealing without greatly influencing a primary sealing in the primary sealing and secondary sealing formed of two hull beads around a cylinder bore.
Further objects and advantages of the invention will be apparent from the following description of the invention.